Fluorescent proteins such as green fluorescent protein (GFP) and Red fluorescent protein (RFP) are valuable tools for biological and biochemical research. For example GFP has been used to analyze bacterial gene expression during infection, to visualize tumor cell behavior during metastasis and to monitor GFP fusion proteins in gene therapy studies. Fluorescent proteins are also useful in high-throughput screening in drug discovery. Red fluorescent protein such as that produced by the coral Discosoma (DsRed) is also potentially useful as a fluorescent reporter protein or as a fusion tag.
There are a variety of known fluorescent proteins that can be used for various biological and biochemical studies (Griesbeck, O., Baird, G. S., Campbell, R. R., Zacharias, D. A., and Tsien, R. Y., (2001) Reducing the environmental sensitivity of yellow fluorescent protein, Mechanism and applications. J. Biol. Chem. 276, 29188-29194; Nagai, T. et al. (2002) A variant of yellow fluorescent protein with fast and efficient maturation for cell-biological applications. Nat. Biotechnol. 20, 87-90; Zapata-hommer, O. and Griesbeck, O. (2003) Efficiently folding and circularly permuted variants of the sapphire mutant of GFP. BMC Biotechnol. 3, 5 Rizzo, M. A., Springer, G. H., Granada, B., and Piston, D. W., (2004) An improved cyan fluorescent protein variant useful FRET. Nat. Biotechnol. 22, 445-449; Shaner, N. C., Campbell, R. E., Steinbach, P. A., Giepmans, B. N. G., Palmer, A. E. and Tsien, R. Y. (2004) Improved monomeric red, orange and yellow fluorescent proteins derived from Discosoma sp. red fluorescent protein. Nat. Biotechnol. 22, 1567-1572; Nguyen, A. W. and Daugherty, P. S. (2005) Evolutionary optimization of fluorescent proteins for intracellular FRET. Nat. Biotechnol. 23, 355-360.
There is still however a need to develop novel fluorescent proteins with different characteristics as experimental and clinical tools. Fluorescent proteins which emit at different wavelengths would be useful for the simultaneous detection of various biochemical parameters.